1. Field of the Invention
The present invention relates to a completely folded body obtained by folding an airbag stored in a steering wheel steered by a driver in a storage shape, and a folding method thereof.
2. Description of the Related Art
In the related art, an airbag stored in a steering wheel is known which is inflated while suppressing the float from longitudinal portions of a ring portion, which is steered by a driver, of the steering wheel in the middle of inflation (for example, see JP-A-2012-6598). In such an airbag, before the airbag is completely inflated, a swinging movement of repeating the contact/separation of the ring portion can be suppressed, and a counterforce from the ring portion can be quickly secured when the inflation of the airbag is completed.
The airbag includes an outer bag forming an outer circumferential wall, and an inner bag provided inside the outer bag. The outer bag is formed by coupling the outer circumferential peripheries of a driver-side wall and a vehicle-side wall on the ring portion side which have substantially circular shape to each other. The vehicle-side wall is provided, in the center, with an inflow opening, which is open to admit an inflation gas to flow inside, and a mounting portion which is disposed in the circumferential periphery of the inflow opening and is used to mount the airbag in a boss portion of the steering wheel. The inner bag includes a central portion which covers the inflow opening of the outer bag, and a front-side arm and a rear-side arm which extend in a tapered shape from the central portion to both front and rear sides. When the inflation gas flows into airbag, the inner bag is inflated prior to the outer bag to press the inner circumferential surface of the outer bag on both tip sides of the front-side arm and the rear-side arm first. Therefore, the swinging movement of repeating the contact/separation of the ring portion can be suppressed before the airbag is completely inflated.
In the conventional completely folded body of an airbag, a front-side folded portion and a rear-side folded portion are disposed on front and rear sides of the upper side of the mounting portion. In the front-side folded portion and the rear-side folded portion, in a state where the inner bag is placed inside, the driver-side wall and the vehicle-side wall of the outer bag are flatly deployed in the overlapped state. A horizontally-shortening folding is performed in a bellows manner and the like such that right and left peripheries are brought to the upper side of the mounting portion and the horizontal width dimension corresponds to the horizontal width dimension of the storage portion. Both front and rear sides are folded to the upper side of the mounting portion in such a manner that front and rear tips are folded to the mounting portion side in the respective central positions of the front end side and the rear end side from the mounting portion, and the tip sides of the folded crease are folded to the mounting portion side, that is, two foldings are performed twice. For this reason, the front-side folded portion and the rear-side folded portion are obtained by folding the front overlapped portion and the rear overlapped portion of the front side and the rear side of the mounting portion in a state where the driver-side wall and the vehicle-side wall of the outer bag are flatly deployed.
The conventional airbag is covered with the airbag cover having a front door and a rear door which are open to both front and rear sides when the breakage expected portion is broken, and stored. Thus, front and rear hinges of the front door and the rear door suppress that both front and rear ends of the airbag protrudes from the storage portion, that is, suppress that respective tips of the front end side and the rear end side of the airbag protrude in the initial inflation. In a subsequent inflation process, it is easily suppressed that the front end side and the rear end side of the airbag float from the front and rear portion of the ring portion.
However, when the completely folded body of the airbag is covered with the airbag cover having the doors which are open to both front and rear sides, the hinges thereof are positioned on the left and right sides, and the front end side and the rear end side of the airbag are disposed in the front and rear sides of portions on the tip side which are largely open in the left and right doors at the initial inflation. For this reason, at the initial inflation, the front end side and the rear end side of the airbag largely protrude from the storage portion, and largely float from the upper surface of the front and rear portion of the ring portion. Thus, it is hard to exert an effect to suppress the swinging before the airbag is completely inflated.
As a countermeasure, it is considered that the front-side folded portion and the rear-side folded portion of the completely folded body of the airbag are roll-folded to be wound from the tip side on the vehicle-side wall side so that the protrusion at the initial inflation can be suppressed by suppressing the release of the folding when the inflation gas flows inside. However, in this case, there is a risk that when the folding is released with the flow of the inflation gas, at least front-side folded portion goes to the lower surface side of the ring portion through the opening provided inside the front portion of the ring portion provided for securing the visibility of meters on the front side of the steering wheel. If front-side folded portion goes to the lower surface side of the ring portion, it results in a situation where the inflated portion of the front-side folded portion cannot be disposed on the upper surface of the ring portion.